This disclosure relates to a thermoplastic composition comprising poly(etherimide-siloxane) copolymers, methods of manufacture, and articles containing the thermoplastic compositions.
Poly(etherimide-siloxane) copolymers (also known as polysiloxane/polyimide block copolymers) have been explored in a wide variety of applications requiring flame retardance, for example as coatings for electrical wires, due to their flame resistant properties and high temperature stability. The copolymers are attractive for applications of this type because the polyetherimide blocks impart desirable properties such as high temperature resistance, high strength, good wear resistance, good flame retardant properties, and low smoke density, while the polysiloxane blocks contribute flexibility, good low-temperature properties, and temperature stability. Even so, it has been difficult to obtain compositions that meet all of the requirements of the most stringent flammability standards, for example the European EN standards.
Aromatic polyketones such as polyaryletherketones are crystalline polymers valued due to their resistance to high temperatures, crystallizability, melt extrudability, and injection moldability, thereby making them versatile and useful in many applications. Crystallization of polymers is an important feature in polymer processing, because the structure developed during crystallization can affect the mechanical and physical properties of the polymer product. The crystallization of polymers under processing conditions is essential for optimizing the processing conditions to obtain a product with desired properties. Aromatic polyketones, such as polyaryletherketones frequently suffer from brittleness, e.g., poor toughness (low ductility), making them unsuitable for many applications. There has been a long felt need to develop a composition that has a ductility that is better than aromatic polyketones and still retains the advantageous processing features found in polyaryletherketone compositions. Polyaryletherketone blends have sought to solve this problem, but these blends have suffered from drawbacks such as insufficient ductility, delamination and the like.
Accordingly, there remains a need in the art for improved thermoplastic compositions having the desired combination of physical properties, including low flammability, low toxicity, and high temperature stability. It has been particularly difficult to obtain these characteristics in combination with high impact strength. It would further be particularly useful if the compositions also have low flexural modulus and high tensile elongation. For some applications, improved tear strength in combination with the foregoing properties would be especially useful.